The 1,1-difluoroethane (CH3CHF2) is attracting attention as, for example, a cryogenic refrigerant or an etching gas.
As for the production and purification methods for 1,1-difluoroethane, the following methods have been conventionally used, for example, (1) a method of reducing chlorinated fluorinated hydrocarbon with hydrogen in the presence of a catalyst (see, Japanese Unexamined Patent Publication No. 7-126197 (JP-A-7-126197)), and (2) a method of fluorinating chloroethylene (CH2═CHCl), 1-chloro-1-fluoroethane or the like in a gas phase by using a fluorination catalyst and reacting unsaturated compounds contained as impurities with an oxide of copper, cobalt, silver, magnesium or the like (see, European Unexamined Patent Publication No. 0370688).
For example, CH3CHF2 (HFC-152a) produced by a method of reacting 1,1-dichloroethane with hydrogen fluoride in the presence of a fluorination catalyst, which is a general production process, or the method of (1) above contains various impurities such as saturated compounds of hydrocarbons (HC), hydrochlorocarbons (HCC), chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFC) or unsaturated compounds.
To obtain high-purity CH3CHF2, these impurities must be removed as far as possible. In particular, chlorine-containing compounds such as hydrochlorocarbon, chlorofluorocarbon and hydrochlorofluorocarbon must, even when difficult to separate by normal distillation, be purified to elevate the purity not only for obtaining a high-purity product but also from the aspect of preventing depletion of the ozone layer. Among those impurities, some compounds form an azeotropic or azeotrope-like mixture with CH3CHF2 and therefore, their separation from CH3CHF2 is very difficult.
For example, regarding the purification of impurities such as 1,1,1,2-tetrafluoroethane (CF3CH2F) and pentafluoroethane (CF3CHF2), which are important as refrigerants, a purification method of removing these compounds by extractive distillation or by dehalogenating hydrogenation using hydrogen in the presence of a catalyst is known. However, the purification method by extractive distillation requires a plurality of expensive facilities such as a distillation tower and this disadvantageously incurs high equipment cost and the like. Also, the purification method using hydrogen has a problem such as high equipment cost and short catalyst life because of the use of a combustible. Furthermore, hydrogen chloride is produced and therefore, the life of the catalyst is shortened.
For the purification of 1,1-difluoroethane, for example, the method of (2) above has been proposed but, in the method of (2), a step of removing the oxidized product is necessary.